Re: [PATCH v4 2/4] mm, proc: account for shmem swap in /proc/pid/smaps

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From	Jerome Marchand <jmarchan@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v4 2/4] mm, proc: account for shmem swap in /proc/pid/smaps
Date	Fri, 02 Oct 2015 17:10:02 +0200
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On 10/02/2015 03:35 PM, Vlastimil Babka wrote:
> Currently, /proc/pid/smaps will always show "Swap: 0 kB" for shmem-backed
> mappings, even if the mapped portion does contain pages that were swapped out.
> This is because unlike private anonymous mappings, shmem does not change pte
> to swap entry, but pte_none when swapping the page out. In the smaps page
> walk, such page thus looks like it was never faulted in.
> 
> This patch changes smaps_pte_entry() to determine the swap status for such
> pte_none entries for shmem mappings, similarly to how mincore_page() does it.
> Swapped out pages are thus accounted for.
> 
> The accounting is arguably still not as precise as for private anonymous
> mappings, since now we will count also pages that the process in question never
> accessed, but only another process populated them and then let them become
> swapped out. I believe it is still less confusing and subtle than not showing
> any swap usage by shmem mappings at all. Also, swapped out pages only becomee a
> performance issue for future accesses, and we cannot predict those for neither
> kind of mapping.

Agreed, this is much better than the current situation. I don't think
there is such a thing as a perfect accounting of shared pages anyway.

> 
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> Acked-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>

Acked-by: Jerome Marchand <jmarchan@redhat.com>

Thread

[PATCH v4 0/4] enhance shmem process and swap accounting Vlastimil Babka <vbabka@suse.cz> - 2015-10-02 15:40 +0200
  [PATCH v4 2/4] mm, proc: account for shmem swap in /proc/pid/smaps Vlastimil Babka <vbabka@suse.cz> - 2015-10-02 15:40 +0200
    Re: [PATCH v4 2/4] mm, proc: account for shmem swap in  /proc/pid/smaps Jerome Marchand <jmarchan@redhat.com> - 2015-10-02 17:10 +0200
    Re: [PATCH v4 2/4] mm, proc: account for shmem swap in  /proc/pid/smaps Michal Hocko <mhocko@kernel.org> - 2015-10-02 17:30 +0200
    Re: [PATCH v4 2/4] mm, proc: account for shmem swap in  /proc/pid/smaps Andrew Morton <akpm@linux-foundation.org> - 2015-10-03 00:40 +0200
    Re: [PATCH v4 2/4] mm, proc: account for shmem swap in  /proc/pid/smaps Hugh Dickins <hughd@google.com> - 2015-10-05 05:10 +0200
    Re: [PATCH v4 2/4] mm, proc: account for shmem swap in  /proc/pid/smaps Peter Zijlstra <peterz@infradead.org> - 2015-10-05 10:00 +0200

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